Quantitative Analysis of the Membrane Affinity of Local Anesthetics Using a Model Cell Membrane

Local anesthesia is a drug that penetrates the nerve cell membrane and binds to the voltage gate sodium channel, inhibiting the membrane potential and neurotransmission. It is mainly used in clinical uses to address the pain of surgical procedures in the local area. Local anesthetics (LAs), however, can be incorporated into the membrane, reducing the thermal stability of the membrane as well as altering membrane properties such as fluidity, permeability, and lipid packing order. The effects of LAs on the membrane are not yet fully understood, despite a number of previous studies. In particular, it is necessary to analyze which is the more dominant factor, the membrane affinity or the structural perturbation of the membrane. To analyze the effects of LAs on the cell membrane and compare the results with those from model membranes, morphological analysis and 50% inhibitory concentration (IC50) measurement of CCD-1064sk (fibroblast, human skin) membranes were carried out for lidocaine (LDC) and tetracaine (TTC), the most popular LAs in clinical use. Furthermore, the membrane affinity of the LAs was quantitatively analyzed using a colorimetric polydiacetylene assay, where the color shift represents their distribution in the membrane. Further, to confirm the membrane affinity and structural effects of the membranes, we performed an electrophysiological study using a model protein (gramicidin A, gA) and measured the channel lifetime of the model protein on the free-standing lipid bilayer according to the concentration of each LA. Our results show that when LAs interact with cell membranes, membrane affinity is a more dominant factor than steric or conformational effects of the membrane.

Drug Conjugation Induced Modulation of Structural and Membrane Interaction Features of Cationic Cell-Permeable Peptides

Cell-penetrating peptides might have great potential for enhancing the therapeutic effect of drug molecules against such dangerous pathogens as Mycobacterium tuberculosis (Mtb), which causes a major health problem worldwide. A set of cationic cell-penetration peptides with various hydrophobicity were selected and synthesized as drug carrier of isoniazid (INH), a first-line antibacterial agent against tuberculosis. Molecular interactions between the peptides and their INH-conjugates with cell-membrane-forming lipid layers composed of DPPC and mycolic acid (a characteristic component of Mtb cell wall) were evaluated, using the Langmuir balance technique. Secondary structure of the INH conjugates was analyzed and compared to that of the native peptides by circular dichroism spectroscopic experiments performed in aqueous and membrane mimetic environment. A correlation was found between the conjugation induced conformational and membrane affinity changes of the INH-peptide conjugates. The degree and mode of interaction were also characterized by AFM imaging of penetrated lipid layers. In vitro biological evaluation was performed with Penetratin and Transportan conjugates. Results showed similar internalization rate into EBC-1 human squamous cell carcinoma, but markedly different subcellular localization and activity on intracellular Mtb.

Rapidly Visualizing the Membrane Affinity of Gene Vectors Using Polydiacetylene-Based Allochroic Vesicles

The high-throughput screening of chemically active substances has aroused widespread interest in recent years. The screening of drug carriers is usually ignored, although they interact directly with physiological barriers and target cells, and they determine the fate and efficacy of drugs in vivo. In this work, a series of polydiacetylene (PDA) vesicles (ca. 550 nm) that simulate the cell membrane are constructed to detect the membrane affinity of gene vectors. The surface potentials of vesicles are adjusted by changing the phospholipid composition using different charged compounds. All vesicles show the rapid color changes upon the addition of gene vectors by the naked eye within <5 min. The optimized 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC)-PDA vesicles display the most sensitive discoloration response to the commercially available gene vectors, including Lipofectamine 2000, Entranster-H4000, and polyethylenimine. The logarithm of transfection efficiency for green fluorescent protein plasmid (pGFP) mediated by these three vectors in L02 and HepG2 cells demonstrate an excellent linear correlation with the logarithm of membrane affinity (log K_b) of the gene vectors detected by DMPC-PDA vesicles. This rapid visualization method not only allows the in vitro membrane affinity prediction of gene vectors that greatly contributes to the gene transfection efficiency, but also offers a universal strategy for the potential high-throughput screening of various carrier materials featuring high cell affinity.

The impact of water on the ambivalent behavior and paradoxical phenomenon of the amyloid-β fibril protein

The crucial role of water in amyloid-β(Aβ) fibril proteins is evaluated in several ways including the water's thermodynamic and kinetic solvation effects. As regards the water's character, its hindered-rotation barriers are also considered. The following protein molecules considered here are: the Aβ40 (PDB ID: 2LMN), Aβ42 (PDB ID: 5KK3 and 2NAO) and the double-layered Aβ17-42 fibril. We discuss: (i) extracellular Aβ40 and Aβ42 fibril monomers exhibit an ambivalent propensity to transform into a helical form toward the N-term region and a β-strand-like form near the C-terminal; (ii) interfacial water molecules play a crucial role in protein-protein interactions, as molecular dynamics simulations have shown a significant impact on the protein-protein binding; (iii) it is shown that the spontaneous dimerization process of the Aβ42 fibril protein in water occurs via a two-step nucleation-accommodation mechanism; (iv) MD simulations of the double-layered Aβ17-42 fibril model show that the C↔C interface appears more energetically favorable than the N↔N interface due to large hydrophobic contacts; (v) the water's role in the HET-s prion and in the Aβ fibrillar aggregates; (vi) it was found that the monomer-oligomer equilibrium spontaneously dissociates into stable monomeric species when they are incubated up to 3 μm for a longer time (>1 week) in a physiological buffer.

An early folding contact between Phe19 and Leu34 is critical for amyloid-β oligomer toxicity

Small hydrophobic oligomers of aggregation-prone proteins are thought to be generically toxic. Here we examine this view by perturbing an early folding contact between Phe19 and Leu34 formed during the aggregation of Alzheimer's amyloid-β (Aβ40) peptide. We find that even conservative single mutations altering this interaction can abolish Aβ40 toxicity. Significantly, the mutants are not distinguishable either by the oligomers size or by the end-state fibrillar structure from the wild type Aβ40. We trace the change in their toxicity to a drastic lowering of membrane affinity. Therefore, nonlocal folding contacts play a key role in steering the oligomeric intermediates through specific conformations with very different properties and toxicity levels. Our results suggest that engineering the folding energy landscape may provide an alternative route to Alzheimer therapeutics.